Demand for electric power generated at power stations is subject to fluctuation depending on the season, the time of day and night, and various means and methods are employed to cope with the changing demand such as by frequently changing and adjusting the amount of power generation according to the demand. As one example of adjusting the amount of power generation, water discharged from a dam during the day is pumped up again using the excess electricity at night to thereby convert the electric energy into potential energy of the water, which is to be utilized once again in power generation. This system is known as pumped storage power generation.
Efficiency in energy conversion in pumped storage power generation is not always high if energy loss during pumping of the water is considered. The system is also defective in that siting of the power station is quite limited.
An attempt has been made to store and utilize the excess electric energy by, for instance, causing a flywheel supported by bearings to continuously rotate with the excess electric energy for an extended period of time.
Since friction of the flywheel must be eliminated with gas to improve the energy efficiency, load of the flywheel acts on the shaft and bearings that are provided beneath the wheel at the center of the rotation to cause frictional force of a great magnitude even if the wheel is rotated under highly reduced pressure. This inevitably causes loss of energy, and it is practically impossible to keep the wheel rotating efficiently for long. When the entire load is designed to be supported by the shaft and bearings provided at the bottom of the wheel, it becomes difficult to make the wheel large and heavy because of the strength of the materials of these component parts.
Further, since the flywheel is supported by the shaft and bearings while being in contact therewith, extraordinary vibrations due to an earthquake and the like would put the flywheel off balance or cause uneven rotation thereof. This would damage the bearings and cause the flywheel to be displaced from the predetermined position of rotation, leading to a potentially disastrous accident.